Hashiwokakero rules: what is and is not allowed

Hashiwokakero (Hashi, Bridges, Ponte) has five rules. They fit on a card, but the edge cases (a bridge over an island, two bridges crossing, a network that splits in two) are where most wrong moves come from. Each rule below has a small diagram of a legal and an illegal position.

The five rules

1. Each circle is an island. Its number is exactly how many bridges end on it.
2. Bridges are straight lines, horizontal or vertical. No diagonals, no bends.
3. Two islands may be joined by one bridge or by two parallel bridges, never three.
4. Bridges never cross each other and never pass over an island.
5. When you finish, every island is reachable from every other: the bridges form one connected network.

Rule 1: the number is exact

A bridge counts once at each end. A double bridge between a 3 and a 2 uses two of the 3 and both of the 2. Finishing an island early, with its number met, is not a mistake; it just means every other direction from it stays empty.

Rule 2: straight lines only

Two islands that share neither a row nor a column can never be joined directly. In a puzzle, each island has at most four neighbours: the nearest island up, down, left and right, if there is one.

Rule 3: at most two bridges per pair

This is why an 8 needs all four of its neighbours with a double bridge to each, and why a 4 in a corner (two neighbours) must send a double bridge each way.

Rule 4: no crossings, no jumping over islands

A bridge also cannot skip an island that sits in its path. If a 2 lies between two islands in the same row, the outer islands are not neighbours; each can only reach the 2.

Rule 5: one network

The connectivity rule is the only rule that cannot be checked one island at a time. It is also what makes harder boards solvable: when finishing a group would cut it off from the rest, that last bridge must go elsewhere. The solving guide calls this the loop rule.

Common questions

Does a puzzle have exactly one solution?

A well-made one does. Every daily board on Causeway is checked by independent programs to have exactly one answer. Some puzzle books and random generators do not guarantee this, which is why you can sometimes reach a finished-looking board that differs from the printed answer. You can test any board you have in the free solver.

Is Hashi the same as Bridges?

Yes. Hashiwokakero is the Japanese name (roughly "build bridges"); Bridges and Hashi are the same puzzle. The rules above are the standard ones used by Nikoli-style books and by most apps.

Ready to play?

Try today's puzzle on Causeway (free, no ads), pick up the patterns on the tips page, or print 12 puzzles.